Preservatives are used to treat wood to resist insect attack and decay. The commercially used preservatives are separated into three basic categories, based primarily on the mode of application, into waterborne, creosote, and oil borne preservatives. Waterborne preservatives include chromated copper arsenate (CCA), ammoniacal copper quat, ammoniacal copper zinc arsenate, and ammoniacal copper arsenate. Wood treated with these chemicals sometimes turns green or grey-green because of a chemical reaction between copper in the preservative and the sun's ultraviolet rays. The preservatives leach into the soil over time, but the copper amines leach from wood at rates several times those observed for CCA.
The primary preserved wood product has historically been southern pine lumber treated with chromated copper arsenate (CCA). Most of this treated lumber was used for decks, fencing and landscape timbers. There has recently been raised concerns about the safety and health effects of CCA as a wood preservative, primarily relating to the arsenic content but also to the chromium content. In 2003/2004, due in part to regulatory guidelines and to concerns about safety, there has been a substantial cessation of use of CCA-treated products. A new generation of copper containing wood preservatives use a form of copper that is soluble. Known preservatives include copper alkanolamine complexes, copper polyaspartic acid complex, alkaline copper quaternary, copper azole, copper boron azole, copper bis(dimethyldithiocarbamate), ammoniacal copper citrate, copper citrate, and the copper ethanolamine carbonate. In practice the principal criteria for commercial acceptance, assuming treatment efficacy, is cost. Of the many copper-amine compositions listed above, only the copper ethanolamine carbonate and ammoniacal copper are in widespread use. There are several problems with these new copper-amine-containing preservatives.
The soluble copper containing wood preservatives are very leachable, compared to CCA. This leaching is of concern for at least two reasons: 1) removal of the copper portion of the pesticide from the wood by leaching will compromise the long term efficacy of the formulation, and 2) the leached copper causes concern that the environment will be contaminated. Copper is extremely toxic to certain fish at sub-part per million levels. One study reported the Synthetic Precipitation Leaching Procedure gave the leachate from CCA-treated wood contained a baseline concentration of about 4 mg copper per liter; leachate from copper (ammonium) boron azole-treated wood contained seven times the baseline; leachate from copper bis(dimethyldithiocarbamate) treated wood had twice the baseline concentration; leachate from alkaline copper quaternary treated wood had over seven times the baseline concentration; and leachate from copper citrate treated wood had over fifteen times the baseline concentration. Copper leaching is such a problem that some states do not allow use of wood treated with the soluble copper containing wood preservatives near waterways.
The commercial soluble copper containing wood preservatives cause increased metal corrosion, for example of nails within the wood. Preserved wood products are often used in load-bearing out-door structures such as decks. Traditional fastening material, including aluminum and standard galvanized fittings, are not suitable for use with wood treated with these new preservatives. Many regions are now specifying that hardware, e.g., fittings, nails, screws, and fasteners, be either galvanized with 1.85 ounces zinc per square foot (a G-185 coating) or require Type 304 stainless steel.
Further, the copper-containing portion of the treatment is not protective against some biological species, and these soluble copper containing wood preservatives require higher copper loading, a second organic biocide, or both to be effective. Indeed, we believe the amines from the copper-amine complex encourage the growth of molds, particularly sapstain molds.
Another concern with soluble copper preservative products generally is that most preservative materials are manufactured at one of several central locations but are used in disparate areas and must be shipped, sometimes substantial distances. The cost of providing and transporting the liquid carrier for these soluble products can be considerable, and the likelihood of an extreme biological impact on fish is very high if transported soluble copper wood preservative material is spilled or accidentally released near a waterway.
Finally, the cost of the amine—between three and 4 moles of amine are required to solubilize a mole of copper) is very high. This application proposes wood preservatives which solve each of these problems.